No description available.

A computer code was written to calculate elastic scattering cross sections using the Klein-Gordon equation. The reason for writing this code is because existing codes do not include relativistic kinematics and therefore are only valid for lower energies. This code was used to analyze alpha particle and pion scattering at relativistic energies upon different target nuclei and to find a relativistic potential for a system at a given energy. The target particles in the alpha study were 12C, 40,42,44,48Ca and other alphas. The pions were incident upon 12C and 40Ca. Optical potentials of different forms were used to compare with previous analyses and the experimental data. The potentials found in this study could be useful to understand the physics underlying other processes such as inelastic and particle transfer reactions. The computer code can be used to extend elastic scattering calculations to angles where data does not exist which can then be compared to future experiments. The code could also be used to create a database of potentials for several systems to study the effects of changing charge, mass or energy of the system.

<p> In the soft photon limit the bremsstrahlung cross-section is related to the corresponding elastic scattering cross-section in a model-independent manner. The cross-section for threshold photoproduction of pions becomes independent of the detailed pion-nucleon interaction if the ratio of pion to nucleon mass is made sufficiently small. These two results are a consequence of the gauge invariance of the scattering amplitude for a process involving one photon. We review the derivation of Low's bremsstrahlung theorem for spin-zero and spin-half particles, and outline an extension to all orders of photon energy. The theorem for photopion production is derived by the same method. A non-relativistic analogue to the Bremsstrahlung theorem is also considered.</p> / Thesis / Master of Science (MSc)

No description available.

Results are presented for a unified analysis of the reactions pp → pp, πd → πd and πd → pp over the center-of-mass energy interval from pion threshold to approximately 2.4 GeV. These results for πd → pp and πd elastic scattering are superior to previous VPI analyses of these reactions. In particular, the overall phase in πd → pp has now been determined. Comparisons and predictions are made with previous (separate and unified) analyses of this two-baryon system. Several partial wave amplitudes show resonance-like behavior in these reactions. / Ph. D.

The resonance spectrum of the nucleon gives direct information on the dynamics and interactions of its constituents. This offers an important challenge to the theoretical models of nucleon structure, including the emerging Lattice QCD predictions, conformal field theories and more phenomenological, QCD-based approaches. Although the various models predict different features for the excitation spectra, the experimental information is currently of too poor quality to differentiate between these models. Pion photoproduction from the nucleon is a powerful probe of the spectrum as most resonances are expected to couple to the pion decay channel. However, cross-sections alone are not sensitive enough to allow identification of the underlying excitation spectrum, as the resonances have energy widths larger than their separations. A major world effort is underway to additionally measure polarisation observables in the production process. For a model-independent analysis a “complete” set of single- and doublepolarisation observables needs to be measured in experiments involving polarised beams, targets and a means of determining recoil nucleon polarisation. In particular, the beam asymmetry is a critical observable for the constraint of partial wave analyses (PWA) used to extract the nucleon excitation spectrum from the data. Almost all of the available world data on the beam asymmetry has been taken on the proton, with the neutron dataset sparse, containing only three experiments at fixed angles and in a limited photon energy range. The lack of extensive data on the neutron is a major deficiency, as different resonances have very different electromagnetic couplings to the proton and neutron. As a result, the data from the two targets will have very different relative contributions from, and sensitivities to, the spectrum of nucleon resonances. Moreover, neutron data is essential for the separation of the isoscalar and isovector components of the reaction amplitudes. This thesis presents a very high statistics measurement of the photon beam asymmetry on the neutron with close-to-complete angular coverage and a wide range of invariant mass (1610 – 2320 MeV) extending over the third resonance region, where the excitation spectrum is particularly ill defined. The experiment was conducted at the Thomas Jefferson National Accelerator Facility (JLab) using a tagged, linearly polarised photon beam, a liquid deuterium target and the CEBAF Large Acceptance Spectrometer (CLAS). The quality and quantity of the data has allowed an invariantmass resolution of 10 MeV and an angular resolution of 0.1 in the cosine of the centre-of-mass pion production angle, θ. Good agreement is evident in the regions where there is kinematic overlap with sparse previous data. Comparison of the new data is made with the two main partial wave analyses, SAID andMAID. Significant discrepancy is observed at backward θ with SAID (across most of the energy range) and MAID (up to ∼ 1750 MeV) and also below ∼ 35◦ in θ with both analyses. This extensive new dataset will help significantly to constrain partial wave analyses and will be a crucial part of the current world effort to use meson photoproduction to tackle long-standing uncertainties in the fundamental excitation spectrum of the nucleon. As a first step towards this the refitting of the SAID partial wave analysis incorporating the new data was carried out and shows very significant changes in the properties of the magnetic P11, P13, D13, D35, F15, G17 and G19 partial waves.

In this thesis we present the work we have done to further the understanding of neutral pion photoproduction from the proton. Our work used heavy-baryon chiral perturbation theory to fourth order, and we explicitly include the ∆(1232) resonance using the delta power-counting scheme. We also test the effects of including and excluding D-waves, partial waves with orbital angular momentum quantum number of 2. We begin our discussion in chapter 1 with a brief history of nuclear physics before showing how current algebras and the partial-conservation of the axial-vector current (PCAC) can be used to describe low-energy hadronic interactions. To improve upon PCAC results, one can make use of chiral effective field theories, taking advantage of the chiral symmetry that is present in the limit of massless quarks. We formally introduce chiral perturbation theory (χPT) in chapter 2, discussing the power-counting problem that arises once baryons are included, and present two different approaches to overcome this. We conclude chapter 2 showing how the theory can be extended to include the ∆(1232) resonance. In chapter 3 we describe the model-independent framework of pion photoproduction needed to describe both theory and experiment. We discuss the various recent efforts to describe pion photoproduction within χPT in the latter half of chapter 3. We lay out the framework we have developed in chapter 4 and present our results in chapter 5. We have compared our work to the recent experimental data released by the A2 and CB-TAPS collaborations at the Mainz Microtron. Our results show that we can accurately describe the data from threshold up to an in-coming laboratory photon energy of approximately 260 MeV, a clear improvement on previous studies. We find that including the ∆ is necessary to describe the data beyond E γ ≈ 200 MeV, but the case for D-waves is not so clear. We cannot pinpoint an energy where their inclusion is necessary but we do find evidence suggesting they are important to improve the stability of the fit. Our best results require the inclusion of both the ∆ and D-waves. Finally, in chapter 6, we present our concluding remarks from what has been achieved over the last four years of study and what forms possible extensions of our work could take.

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Bibliography : leaves 135-146 / vii, 146 leaves ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1991

Bibliography :leaves 144-[148] / xiv, [148] leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1993